Omeprazole is a substituted benzimidazole, 5-methoxy-2-[(4-methoxy-3,5-dimethyl-2-pyridinyl) methyl]sulfinyl]-1H-benzimidazole, that inhibits gastric acid secretion. Omeprazole belongs to a class of antisecretory compounds called proton pump inhibitors (“PPIs”) that do not exhibit anti-cholinergic or H2 histamine antagonist properties. Drugs of this class suppress gastric acid secretion by the specific inhibition of the H+,K+-ATPase enzyme system (proton pump) at the secretory surface of the gastric parietal cell.
Typically, omeprazole, lansoprazole and other proton pump inhibitors are formulated in an enteric-coated solid dosage form (as either a delayed-release capsule or tablet) or as an intravenous solution (or as a product for reconstitution), and are prescribed for short-term treatment of active duodenal ulcers, gastric ulcers, gastroesophageal reflux disease (GERD), severe erosive esophagitis, poorly responsive systematic GERD, and pathological hypersecretory conditions such as Zollinger Ellison syndrome. These conditions are caused by an imbalance between acid and pepsin production, called aggressive factors, and mucous, bicarbonate, and prostaglandin production, called defensive factors. These above-listed conditions commonly arise in healthy or critically ill patients, and may be accompanied by significant upper gastrointestinal bleeding.
H2-antagonists, antacids, and sucralfate are commonly administered to minimize the pain and the complications related to these conditions. These drugs have certain disadvantages associated with their use. Some of these drugs are not completely effective in the treatment of the aforementioned conditions and/or produce adverse side effects, such as mental confusion, constipation, diarrhea, and thrombocytopenia. H2-antagonists, such as ranitidine and cimetidine, are relatively costly modes of therapy, particularly in NPO patients, which frequently require the use of automated infusion pumps for continuous intravenous infusion of the drug.
Patients with significant physiologic stress are at risk for stress-related gastric mucosal damage and subsequent upper gastrointestinal bleeding (Marrone and Silen, Pathogenesis, Diagnosis and Treatment of A cute Gastric Mucosa Lesions, CLIN GASTROENTEROL 13: 635-650 (1984)). Risk factors that have been clearly associated with the development of stress-related mucosal damage are mechanical ventilation, coagulopathy, extensive burns, head injury, and organ transplant (Zinner et al., The Prevention of Gastrointestinal Tract Bleeding in Patients in an Intensive Care Unit, SURG. GYNECOL. OBSTET., 153: 214-220 (1981); Larson et al., Gastric Response to Severe Head Injury, AM. J. SURG. 147: 97-105 (1984); Czaja et al., Acute Gastroduodenal Disease After Thermal Injury: An Endoscopic Evaluation of Incidence and Natural History, N ENGL. J. MED, 291: 925-929 (1974); Skillman et at., Respiratory Failure, Hypotension, Sepsis and Jaundice. A Clinical Syndrome Associated with Lethal Hemorrhage From Acute Stress Ulceration, AM. J. SURG., 117:523-530(1969); and Cook et al., Risk Factors for Gastrointestinal Bleeding in Critically Ill Patients, N. ENGL. J. MED., 330:377-38 1 (1994)). One or more of these factors are often found in critically ill, intensive care unit patients. A recent cohort study challenges other risk factors previously identified such as acid-base disorders, multiple trauma, significant hypertension, major surgery, multiple operative procedures, acute renal failure, sepsis, and coma (Cook et at., Risk Factors for Gastrointestinal Bleeding in Critically Ill Patients, N. ENGL. J. MED., 330:377-381 (1994)). Regardless of the risk type, stress-related mucosal damage results in significant morbidity and mortality. Clinically significant bleeding occurs in at least twenty percent of patients with one or more risk factors who are left untreated (Martin et at., Continuous Intravenous Cimetidine Decreases Stress-related Upper Gastro-intestinal Hemorrhage Without Promoting Pneumonia, CRIT. CARE MED., 21: 19-30(1993)). Of those who bleed, approximately ten percent require surgery (usually gastrectomy) with a reported mortality of thirty percent to fifty percent (Czaja et al., Acute Gastroduodenal Disease After Thermal Injury: An Endoscopic Evaluation of Incidence and Natural History, N ENGL. J. MED, 291: 925-929 (1974); Peura and Johnson, Cimetidine for Prevention and Treatment of Gastroduodenal Mucosal Lesions in Patients in an Intensive Care Unit, ANN INTERN MED., 103: 173-177 (1985)). Those who do not need surgery often require multiple transfusions and prolonged hospitalization. Prevention of stress-related upper gastrointestinal bleeding is an important clinical goal.
In addition to general supportive care, the use of drugs to prevent stress-related mucosal damage and related complications is considered by many to be the standard of care (AMA Drug Evaluations). However, general consensus is lacking about which drugs to use in this setting (Martin et al., Continuous Intravenous Cimetidine Decreases Stress-related Upper Gastrointestinal Hemorrhage Without Promoting Pneumonia, CRIT. CARE MED., 21: 19-30 (1993); Gafter et al., Thrombocytopenia Associated With Hypersensitivity to Ranitidine: Possible Cross-reactivity with Cimetidine, AM. J. GASTROENTEROL, 84: 560-562 (1989); Martin et al., Stress Ulcers and Organ Failure in Intubated Patients in Surgical Intensive Care Units, ANN SURG., 215: 332-337 (1992)). In two recent meta-analyses (Cook et al., Stress Ulcer Prophylaxis in the Critically Ill: A Meta-analysis, AM. J. MED., 91: 519-527 (1991); Tryba, Stress Ulcer Prophylaxis—Quo Vadis? INTENS. CARE MED. 20: 311-313 (1994)) antacids, sucralfate, and H2-antagonists were all found to be superior to placebo and similar to one another in preventing upper gastrointestinal bleeding. Yet, prophylactic agents are withdrawn in fifteen to twenty percent of patients in which they are employed because of failure to prevent bleeding or control pH (Ostro et al., Control of Gastric pH With Cimetidine Boluses Versus Primed Infusions, GASTROENTEROLOGY, 89: 532-537 (1985); Siepler, A Dosage Alternative for H-2 Receptor Antagonists, Continuous-Infusion, CLIN. THER., 8(SUPPL A): 24-33 (1986); Ballesteros et al., Bolus or Intravenous Infusion of Ranitidine: Effects on Gastric pH and Acid Secretion: A Comparison of Relative Cost and Efficacy, ANN. INTERN. MED., 112:334-339 (1990)), or because of adverse effects (Gafter et al., Thrombocytopenia Associated With Hypersensitivity to Ranitidine: Possible Cross-reactivity With Cimetidine, AM. J. GASTROENTEROL, 84: 560-562 (1989); Sax, Clinically Important Adverse Effects and Drug Interactions With H2-Receptor Antagonists: An Update, PHARMACOTHERAPY 7(6 PT 2): 1105-1155 (1987); Vial et al., Side Effects of Ranitidine, DRUG SAF, 6:94-117(1991); Cantu and Korek, Central Nervous System Reactions to Histamine-2 Receptor Blockers, ANN. ITERN MED., 114:1027-1034 (1991); and Spychal and Wickham, Thrombocytopenia Associated With Ranitidine, BR. MED. J., 291:1687 (1985)). In addition, the characteristics of an ideal agent for the prophylaxis of stress gastritis were analyzed by Smythe and Zarowitz, Changing Perspectives of Stress Gastritis Prophylaxis, ANN PHARMACOTHER, 28: 1073-1084 (1994) who concluded that none of the agents currently in use fulfill their criteria.
Stress ulcer prophylaxis has become routine therapy in intensive care units in most hospitals (Fabian et al., Pneumonia and Stress Ulceration in Severely Injured Patients, ARCH. SURG., 128: 185-191 (1993); Cook et al., Stress Ulcer Prophylaxis in the Critically Ill: A Meta-Analysis, AM. J. MED., 91: 519-527 (1991)). Controversy remains regarding pharmacologic intervention to prevent stress-related bleeding in critical care patients. It has been suggested that the incidence and risk of gastrointestinal bleeding has decreased in the last ten years and drug therapy may no longer be needed (Cook et al., Risk Factors for Gastrointestinal Bleeding in Critically Ill Patients, N. ENGL. J. MED., 330:377-381 (1994); Tryba, Stress Ulcer Prophylaxis—Quo Vadis? INTENS. CARE MED. 20: 311-313 (1994); Schepp, Stress Ulcer Prophylaxis: Still a Valid Option in the 1990s?, DIGESTION 54: 189-199 (1993)). This reasoning is not supported by a recent placebo-controlled study. Martin et al. conducted a prospective, randomized, double-blind, placebo-controlled comparison of continuous-infusion cimetidine and placebo for the prophylaxis of stress-related mucosal damage. The study was terminated early because of excessive bleeding-related mortality in the placebo group. It appears that the natural course of stress-related mucosal damage in a patient at risk who receives no prophylaxis remains significant. In the placebo group, thirty-three percent (33%) of patients developed clinically significant bleeding, nine percent (9%) required transfusion, and six percent (6%) died due to bleeding-related complications. In comparison, fourteen percent (14%) of cimetidine-treated patients developed clinically significant bleeding, six percent (6%) required transfusions, and one and one-half percent (1.5%) died due to bleeding-related complication. The difference in bleeding rates between treatment groups was statistically significant. This study clearly demonstrated that continuous-infusion cimetidine reduced morbidity in critical care patients. Although these data were used to support the approval of continuous-infusion cimetidine by the Food and Drug Administration for stress ulcer prophylaxis, H2-antagonists fall short of being the optimal pharmacotherapeutic agents for preventing of stress-related mucosal bleeding.
Another controversy surrounding stress ulcer prophylaxis is which drug to use. In addition to the various H2-antagonists, antacids and sucralfate are other treatment options for the prophylaxis of stress-related mucosal damage. An ideal drug in this setting should possess the following characteristics: prevent stress ulcers and their complications, be devoid of toxicity, lack drug interactions, be selective, have minimal associated costs (such as personnel time and materials), and be easy to administer (Smythe and Zarowitz, Changing Perspectives of Stress Gastritis Orophylaxis, ANN PHARMACOTHER, 28: 1073-1084 (1994)). Some have suggested that sucralfate is possibly the ideal agent for stress ulcer prophylaxis (Smythe and Zarowitz, Changing Perspectives of Stress Gastritis Prophylaxis, ANN PHARMACOTHER, 28: 1073-1084 (1994)). Randomized, controlled studies support the use of sucralfate (Borrero et al., Antacids vs. Sucralfate in Preventing Acute Gastrointestinal Tract Bleeding in Abdominal Aortic Aurgery, ARCH. SURG., 121: 810-812 (1986); Tryba, Risk of Acute Stress Bleeding and Nosocomial Pneumonia in Ventilated Intensive Care Patients. Sucralfate vs. Antacids, AM. J. MED., 87(3B): 117-124 (1987); Cioffi et al., Comparison of Acid Neutralizing and Non-acid Neutralizing Stress Ulcer Prophylaxis in Thermally Injured Patients. J. TRAUMA, 36: 541-547 (1994); and Driks et al., Nosocomial Pneumonia in Intubated Patients Given Sucralfate as Compared With Antacids or Histamine Type 2 Blockers, N. ENGL. J. MED., 317: 1376-1382 1987)), but data on critical care patients with head injury, trauma, or burns are limited. In addition, a recent study comparing sucralfate and cimetidine plus antacids for stress ulcer prophylaxis reported clinically significant bleeding in three of forty-eight (6%) sucralfate-treated patients, one of whom required a gastrectomy (Cioffi et al., Comparison of Acid Neutralizing and Non-acid Neutralizing Stress Ulcer Prophylaxis in Thermally Injured Patients, J. TRAUMA, 36: 541-547 (1994)). In the study performed by Driks and coworkers that compared sucralfate to conventional therapy (H2-antagonists, antacids, or H2-antagonists plus antacids), the only patient whose death was attributed to stress-related upper gastrointestinal bleeding was in the sucralfate arm (Driks et al., Nosocomial Pneumonia in Intubated Patients Given Sucralfate as Compared With Antacids or Histamine Type 2 Blockers, N. ENGL. J. MED., 317: 1376-1382 (1987)).
H2-antagonists fulfill many of the criteria for an ideal stress ulcer prophylaxis drug. Yet, clinically significant bleeds can occur during H2-antagonist prophylaxis (Martin et al., Continuous Intravenous Cimetidine Decreases Stress-related Upper Gastrointestinal Hemorrhage Without Promoting Pneumonia, CRIT. CARE MED., 21: 19-39 (1993); Cook et al., Stress Ulcer Prophylaxis in the Critically Ill: A Meta-analysis, AM. J. MED., 91: 519-527 (1991); Schuman et al., Prophylactic Therapy for Acute Ulcer Bleeding: A Reappraisal, ANN INTERN. MED, 106: 562-567 (1987)). Adverse events are not uncommon in the critical care population (Gafter et al., Thrombocytopenia Associated With Hypersensitivity to Ranitidine: Possible Cross-Reactivity With Cimetidine, AM. J. GASTROENTEROL, 64: 560-562 (1989); Sax, Clinically Important Adverse Effects and Drug Interactions With H2-receptor Antagonists: An Update, PHARMACOTHERAPY 7 (6 PT 2): 110S-115S (1987); Vial et al., Side Effects of Ranitidine, DRUG SAF., 6:94-117 (1991); Cantu and Korek, Central Nervous System Reactions to Histamine-2 Receptor Blockers, ANN. INTERN MED., 114: 1027-1034 (1991); Spychal and Wickham, Thrombocytopenia Associated With Ranitidine, BR. MED. J., 291: 1687 (1985)).
One reason proposed for the therapeutic H2-antagonist failures is lack of pH control throughout the treatment period (Ostro et al., Control of Gastric pH With Cimetidine Boluses Versus Primed Infusions, GASTROENTEROLOGY, 89: 532-537 (1985)). Although the precise pathophysiologic mechanisms involved in stress ulceration are not clearly established, the high concentration of hydrogen ions in the mucosa (Fiddian-Green et al., 1987) or gastric fluid in contact with mucosal cells appears to be an important factor. A gastric pH>3.5 has been associated with a lower incidence of stress-related mucosal damage and bleeding (Larson et al., Gastric Response to Severe Head Injury, AM. J. SURG. 147: 97-105 (1984); Skillman et al., Respiratory Failure, Hypotension, Sepsis and Jaundice: A Clinical Syndrome Associated With Lethal Hemorrhage From Acute Stress Ulceration, AM. J. SURG., 117: 523-530 (1969); Skillman et al., The Gastric Mucosal Barrier: Clinical and Experimental Studies in Critically Ill and Normal Man and in the Rabbit, ANN SURG., 172: 564-584 (1970); and Priebe and Skillman, Methods of Prophylaxis in Stress Ulcer Disease, WORLD J. SURG., 5: 223-233 (1981)). Several studies have shown that H2-antagonists, even in maximal doses, do not reliably or continuously increase intragastric pH above commonly targeted levels (3.5 to 4.5). This is true especially when used in fixed-dose bolus regimens (Ostro et al., Control of Gastric pH With Cimetidine Boluses Versus Primed Infusions, GASTROENTEROLOGY, 89: 532-537 (1985); Siepler, A Dosage Alternative for H-2 Receptor Antagonists, Continuous-infusion, CLIN. THER., 8(SUPPL A): 24-33 (1986); Ballesteros et al., Bolus or Intravenous Infusion of Ranitidine: Effects on Gastric pH and Acid Secretion: A Comparison of Relative Cost and Efficacy, ANN. INTERN. MED., 112:334-339 (1990)). In addition, gastric pH levels tend to trend downward with time when using a continuous-infusion of H2-antagonists, which may be the result of tachyphylaxis (Ostro et al., Control of Gastric pH With Cimetidine Boluses Versus Primed Infusions, GASTROENTEROLOGY, 89: 532-537 (1985); Wilder-Smith and Merki, Tolerance During Dosing With H2-receptor Antagonists. An Overview, SCAND. J. GASTROENTEROL 27 (SUPPL. 193): 14-19 (1992)).
Because stress ulcer prophylaxis is frequently employed in the intensive care unit, it is essential from both a clinical and economic standpoint to optimize the pharmacotherapeutic approach. In an attempt to identify optimal therapy, cost of care becomes an issue. All treatment costs should be considered, including the costs of treatment failures and drug-related adverse events. While the actual number of failures resulting in mortality is low, morbidity (e.g., bleeding that requires blood transfusion) can be high, even though its association with the failure of a specific drug is often unrecognized.
Initial reports of increased frequency of pneumonia in patients receiving stress ulcer prophylaxis with agents that raise gastric pH has influenced the pharmacotherapeutic approach to management of critical care patients. However, several recent studies (Simms et al., Role of Gastric Colonization in the Development of Pneumonia in Critically Ill Trauma Patients: Results of a Prospective Randomized Trial, J. TRAUMA, 31: 531-536 (1991); Pickworth et al., Occurrence of Nasocomial Pneumonia in Mechanically Ventilated Trauma Patients: A Comparison of Sucralfate and Ranitidine, CRIT. CARE MED., 12: 1856-1862 (1993); Ryan et al., Nasocomial Pneumonia During Stress Ulcer Prophylaxis With Cimetidine and Sucralfate, ARCH. SURG., 128: 1353-1357 (1993); Fabian et al., Pneumonia and Stress Ulceration in Severely Injured Patients, ARCH. SURG., 128: 185-191 (1993)), a meta-analysis (Cook et al., Stress Ulcer Prophylaxis in the Critically Ill: A Meta-analysis, AM. J. MED., 91: 519-527 (1991)), and a closer examination of the studies that initiated the elevated pH-associated pneumonia hypotheses (Schepp, Stress Ulcer Prophylaxis: Still a Valid Option in the 1990s?, DIGESTION 54: 189-199 (1993)) cast doubt on a causal relationship. The relationship between pneumonia and antacid therapy is much stronger than for H2-antagonists. The shared effect of antacids and H2-antagonists on gastric pH seems an irresistible common cause explanation for nosocomial pneumonia observed during stress ulcer prophylaxis. However, there are important differences between these agents that are not often emphasized (Laggner et al., Prevention of Upper Gastrointestinal Bleeding in Long-term Ventilated Patients, AM. J. MED., 86 (SUPPL 6A): 81-84 (1989)). When antacids are exclusively used to control pH in the prophylaxis of stress-related upper gastrointestinal bleeding, large volumes are needed. Volume, with or without subsequent reflux, may be the underlying mechanism(s) promoting the development of pneumonia in susceptible patient populations rather than the increased gastric pH. The rate of pneumonia (12%) was not unexpected in this critical care population and compares with sucralfate, which does not significantly raise gastric pH (Pickworth et al., Occurrence of Nasocomial Pneumonia in Mechanically Ventilated Trauma Patients: A Comparison of Sucralfate and Ranitidine, CRIT. CARE MED., 12: 1856-1862 (1993); Ryan et al., Nasocomial Pneumonia During Stress Ulcer Prophylaxis With Cimetidine and Sucralfate, ARCH. SURG., 128: 1353-1357 (1993)).
Omeprazole (Prilosec®), lansoprazole (Prevacid®) and other PPIs reduce gastric acid production by inhibiting H+,K+-ATPase of the parietal cell—the final common pathway for gastric acid secretion (Fellenius et al., Substituted Benzimidazoles Inhibit Gastric Acid Secretion by Blocking H+,K+-ATPase, NATURE, 290: 159-161 (1981); Wallmark et al, The Relationship Between Gastric Acid Secretion and Gastric H+,K+-ATPase Activity, J. BIOL. CHEM., 260: 13681-13684 (1985); Fryklund et al., Function and Structure of Parietal Cells After H+,K+-ATPase Blockade, AM. J. PHYSIOL., 254 (3 PT 1); G399-407 (1988)).
PPIs contain a sulfinyl group in a bridge between substituted benzimidazole and pyridine rings, as illustrated below.

At neutral pH, omeprazole, lansoprazole and other PPIs are chemically stable, lipid-soluble, weak bases that are devoid of inhibitory activity. These neutral weak bases reach parietal cells from the blood and diffuse into the secretory canaliculi, where the drugs become protonated and thereby trapped. The protonated agent rearranges to form a sulfenic acid and a sulfenamide. The sulfenamide interacts covalently with sulfhydryl groups at critical sites in the extracellular (luminal) domain of the membrane-spanning H+,K+-ATPase (Hardman et al., Goodman & Gilman's The Pharmacological Basis of Therapeutics, p. 907 (9th ed. 1996)). Omeprazole and lansoprazole, therefore, are prodrugs that must be activated to be effective. The specificity of the effects of PPIs is also dependent upon: (a) the selective distribution of H+,K+-ATPase; (b) the requirement for acidic conditions to catalyze generation of the reactive inhibitor; and (c) the trapping of the protonated drug and the cationic sulfenamide within the acidic canaliculi and adjacent to the target enzyme. (Hardman et al., 1996)).
Omeprazole and lansoprazole are available for oral administration as enteric coated particles in gelatin capsules. Other proton pump inhibitors such as rabeprazole and pantoprazole are supplied as enteric coated tablets. The enteric dosage forms of the prior art have been employed because it is very important that these drugs not be exposed to gastric acid prior to absorption. Although these drugs are stable at alkaline pH, they are destroyed rapidly as pH falls (e.g., by gastric acid). Therefore, if the microencapsulation or the enteric coating is disrupted (e.g., trituration to compound a liquid, or chewing the capsule), the drug will be exposed to degradation by the gastric acid in the stomach.
The absence of an intravenous or oral liquid dosage form in the United States has limited the testing and use of omeprazole, lansoprazole and rabeprazole in the critical care patient population. Barie et al., Therapeutic Use of Omeprazole for Refractory Stress-induced Gastric Mucosal Hemorrhage, CRIT. CARE MED., 20: 899-901 (1992) have described the use of omeprazole enteric-coated pellets administered through a nasogastric tube to control gastrointestinal hemorrhage in a critical care patient with multi-organ failure. However, such pellets are not ideal as they can aggregate and occlude such tubes, and they are not suitable for patients who cannot swallow the pellets. AM J. HEALTH-SYST PHARM 56:2327-30 (1999).
Proton pump inhibitors such as omeprazole represent an advantageous alternative to the use of H2-antagonists, antacids, and sucralfate as a treatment for complications related to stress-related mucosal damage. However, in their current form (capsules containing enteric-coated granules or enteric-coated tablets), proton pump inhibitors can be difficult or impossible to administer to patients who are either unwilling or unable to swallow tablets or capsules, such as critically ill patients, children, the elderly, and patients suffering from dysphagia. Therefore, it would be desirable to formulate a proton pump inhibitor solution or suspension which can be enterally delivered to a patient thereby providing the benefits of the proton pump inhibitor without the drawbacks of the current enteric-coated solid dosage forms.
Omeprazole, the first proton pump inhibitor introduced into use, has been formulated in many different embodiments such as in a mixture of polyethylene glycols, adeps solidus and sodium lauryl sulfate in a soluble, basic amino acid to yield a formulation designed for administration in the rectum as taught by U.S. Pat. No. 5,219,870 to Kim.
U.S. Pat. No. 5,395,323 to Berglund ('323) discloses a device for mixing a pharmaceutical from a solid supply into a parenterally acceptable liquid form for parenteral administration to a patient. The '323 patent teaches the use of an omeprazole tablet which is placed in the device and dissolved by normal saline, and infused parenterally into the patient. This device and method of parenteral infusion of omeprazole does not provide the omeprazole solution as an enteral product, nor is this omeprazole solution directly administered to the diseased or affected areas, namely the stomach and upper gastrointestinal tract, nor does this omeprazole formulation provide the immediate antacid effect of the present formulation.
U.S. Pat. No. 4,786,505 to Lovgren et al. discloses a pharmaceutical preparation containing omeprazole together with an alkaline reacting compound or an alkaline salt of omeprazole optionally together with an alkaline compound as a core material in a tablet formulation. The use of the alkaline material, which can be chosen from such substances as the sodium salt of carbonic acid, are used to form a “micro-pH” around each omeprazole particle to protect the omeprazole which is highly sensitive to acid pH. The powder mixture is then formulated to small beads, pellets, tablets and may be loaded into capsules by conventional pharmaceutical procedures. This formulation of omeprazole does not provide an omeprazole dosage form which can be enterally administered to a patient who may be unable and/or unwilling to swallow capsules, tablets or pellets, nor does it teach a convenient form which can be used to make an omeprazole or other proton pump inhibitor solution or suspension.
Several buffered omeprazole oral solutions/suspensions have been disclosed. For example, Pilbrant et al., Development of an Oral Formulation of Omeprazole, SCAND. J. GASTROENT. 20(Suppl. 108): 113-120 (1985) teaches the use of micronized omeprazole suspended in water, methylcellulose and sodium bicarbonate in a concentration of approximately 1.2 mg omeprazole/ml suspension.
Andersson et el., Pharmacokinetics of Various Single Intravenous and Oral Doses of Omeprazole, EUR J. CLIN. PHARMACOL. 39: 195-197 (1990) discloses 10 mg, 40 mg, and 90 mg of oral omeprazole dissolved in PEG 400, sodium bicarbonate and water. The concentration of omeprazole cannot be determined as volumes of diluent are not disclosed. Nevertheless, it is apparent from this reference that multiple doses of sodium bicarbonate were administered with and after the omeprazole suspension.
Andersson et al., Pharmacokinetics and Bioavailability of Omeprazole After Single and Repeated Oral Administration in Healthy Subjects, BR. J. CLIN. PHARMAC. 29: 557-63 (1990) teaches the oral use of 20 mg of omeprazole, which was dissolved in 20 g of PEG 400 (sp. gravity=1.14) and diluted with 50 ml of sodium bicarbonate, resulting in a concentration of 0.3 mg/ml.
Regardh et al., The Pharmacokinetics of Omeprazole in Humans-A Study of Single Intravenous and Oral Doses, THER. DRUG MON. 12: 163-72 (1990) discloses an oral dose of omeprazole at a concentration 0.4 mg/ml after the drug was dissolved in PEG 400, water and sodium bicarbonate.
Landahl et al., Pharmacokinetics Study of Omeprazole in Elderly Healthy Volunteers, CLIN. PHARMACOKINETICS 23 (6): 469-476 (1992) teaches the use of an oral dose of 40 mg of omeprazole dissolved in PEG 400, sodium bicarbonate and water. This reference does not disclose the final concentrations utilized. Again, this reference teaches the multiple administration of sodium bicarbonate after the omeprazole solution.
Andersson et al., Pharmacokinetics of [14C] Omeprazole in Patients with Liver Cirrhosis, CLIN. PHARMACOKINETICS 24 (1): 71-78 (1993) discloses the oral administration of 40 mg of omeprazole which was dissolved in PEG 400, water and sodium bicarbonate. This reference does not teach the final concentration of the omeprazole solution administered, although it emphasizes the need for concomitant sodium bicarbonate dosing to prevent acid degradation of the drug.
Nakagawa, et al., Lansoprazole: Phase I Study of lansoprazole (AG-1749) Anti-ulcer Agent, J. CLIN. THERAPEUTICS & MED. (1991) teaches the oral administration of 30 mg of lansoprazole suspended in 100 ml of sodium bicarbonate (0.3 mg/ml), which was administered to patients through a nasogastric tube.
All of the buffered omeprazole solutions described in these references were administered orally, and were given to healthy subjects who were able to ingest the oral dose. In all of these studies, omeprazole was suspended in a solution including sodium bicarbonate, as a pH buffer, in order to protect the acid sensitive omeprazole during administration. In all of these studies, repeated administration of sodium bicarbonate both prior to, during, and following omeprazole administration were required in order to prevent acid degradation of the omeprazole given via the oral route of administration. In the above-cited studies, as much as 48 mmoles of sodium bicarbonate in 300 ml of water must be ingested for a single dose of omeprazole to be orally administered.
The buffered omeprazole solutions of the above cited prior art require the ingestion of large amounts of sodium bicarbonate and large volumes of water by repeated administration. This has been considered necessary to prevent acid degradation of the omeprazole. In the above-cited studies, basically healthy volunteers, rather than sick patients, were given dilute buffered omeprazole utilizing pre-dosing and post-dosing with large volumes of sodium bicarbonate.
The administration of large amounts of sodium bicarbonate can produce at least six significant adverse effects, which can dramatically reduce the efficacy of the omeprazole in patients and reduce the overall health of the patients. First, the fluid volumes of these dosing protocols would not be suitable for sick or critically ill patients who must receive multiple doses of omeprazole. The large volumes would result in the distention of the stomach and increase the likelihood of complications in critically ill patients such as the aspiration of gastric contents.
Second, because bicarbonate is usually neutralized in the stomach or is absorbed, such that belching results, patients with gastroesophageal reflux may exacerbate or worsen their reflux disease as the belching can cause upward movement of stomach acid (Goodman AG, et al., Agents for the Control of Gastric Acidity and Treatment of Peptic Ulcers, in, THE PHARMACOLOGIC BASIS OF THERAPEUTICS (New York, p. 907 (1990)).
Third, patients with conditions such as hypertension or heart failure are standardly advised to avoid the intake of excessive sodium as it can cause aggravation or exacerbation of their hypertensive conditions (Brunton, supra). The ingestion of large amounts of sodium bicarbonate is inconsistent with this advice.
Fourth, patients with numerous conditions that typically accompany critical illness should avoid the intake of excessive sodium bicarbonate as it can cause metabolic alkalosis that can result in a serious worsening of the patient's condition.
Fifth, excessive antacid intake (such as sodium bicarbonate) can result in drug interactions that produce serious adverse effects. For example, by altering gastric and urinary pH, antacids can alter rates of drug dissolution and absorption, bioavailability, and renal elimination (Brunton, supra).
Sixth, because the buffered omeprazole solutions of the prior art require prolonged administration of sodium bicarbonate, it makes it difficult for patients to comply with the regimens of the prior art. For example, Pilbrant et al. disclose an oral omeprazole administration protocol calling for the administration to a subject who has been fasting for at least ten hours, a solution of 8 mmoles of sodium bicarbonate in 50 ml of water. Five minutes later, the subject ingests a suspension of 60 mg of omeprazole in 50 ml of water that also contains 8 mmoles of sodium bicarbonate. This is rinsed down with another 50 ml of 8 mmoles sodium bicarbonate solution. Ten minutes after the ingestion of the omeprazole dose, the subject ingests 50 ml of bicarbonate solution (8 mmoles). This is repeated at twenty minutes and thirty minutes post omeprazole dosing to yield a total of 48 mmoles of sodium bicarbonate and 300 ml of water in total which are ingested by the subject for a single omeprazole dose. Not only does this regimen require the ingestion of excessive amounts of bicarbonate and water, which is likely to be dangerous to some patients, it is unlikely that even healthy patients would comply with this regimen.
It is well documented that patients who are required to follow complex schedules for drug administration are non-compliant and, thus, the efficacy of the buffered omeprazole solutions of the prior art would be expected to be reduced due to non-compliance. Compliance has been found to be markedly reduced when patients are required to deviate from a schedule of one or two (usually morning and night) doses of a medication per day. The use of the prior art buffered omeprazole solutions which require administration protocols with numerous steps, different drugs (sodium bicarbonate+omeprazole+PEG 400 versus sodium bicarbonate alone), and specific time allotments between each stage of the total omeprazole regimen in order to achieve efficacious results is clearly in contrast with both current drug compliance theories and human nature.
The prior art (Pilbrant et al., 1985) teaches that the buffered omeprazole suspension can be stored at refrigerator temperatures for a week and deep frozen for a year while still maintaining 99% of its initial potency. It would be desirable to have an omeprazole or other proton pump inhibitor solution or suspension that could be stored at room temperature or in a refrigerator for periods of time which exceed those of the prior art while still maintaining 99% of the initial potency. Additionally, it would be advantageous to have a form of the omeprazole and bicarbonate which can be utilized to instantly make the omeprazole solution/suspension of the present invention which is supplied in a solid form which imparts the advantages of improved shelf-life at room temperature, lower cost to produce, less expensive shipping costs, and which is less expensive to store.
It would, therefore, be desirable to have a proton pump inhibitor formulation, which provides a cost-effective means for the treatment of the aforementioned conditions without the adverse effect profile of H2 receptor antagonists, antacids, and sucralfate. Further, it would be desirable to have a proton pump inhibitor formulation which is convenient to prepare and administer to patients unable to ingest solid dosage forms such as tablets or capsules, which is rapidly absorbed, and can be orally or enterally delivered as a liquid form or solid form. It is desirable that the liquid formulation not clog indwelling tubes, such as nasogastric tubes or other similar tubes, and which acts as an antacid immediately upon delivery.
It would further be advantageous to have a potentiator or enhancer of the pharmacological activity of the PPIs. It has been theorized by applicant that the PPIs can only exert their effects on H+,K+-ATPase when the parietal cells are active. Accordingly, applicant has identified, as discussed below, parietal cell activators that are administered to synergistically enhance the activity of the PPIs.
Additionally, the intravenous dosage forms of PPIs of the prior art are often administered in larger doses than the oral forms. For example, the typical adult IV dose of omeprazole is greater than 100 mg/day whereas the adult oral dose is 20 to 40 mg/day. Large IV doses are necessary to achieve the desired pharmacologic effect because, it is believed, many of the parietal cells are in a resting phase (mostly inactive) during an IV dose given to patients who are not taking oral substances by mouth (npo) and, therefore, there is little active (that which is inserted into the secretory canalicular membrane) H+,K+-ATPase to inhibit. Because of the clear disparity in the amount of drug necessary for IV versus oral doses, it would be very advantageous to have compositions and methods for IV administration where significantly less drug is required.